This invention relates to hydrofluorocarbons useful in refrigeration and heat pump applications as well as foam blowing agents. More specifically, the invention provides hydrofluorocarbons that are environmentally desirable replacements for chlorofluorocarbons and hydrochlorofluorocarbons in refrigeration applications, such as centrifugal chillers, particularly multi-stage centrifugal chillers, and foam blowing agent applications.
Fluorocarbon based fluids have found widespread use in industry for refrigeration applications such as air conditioning and heat pump applications.
Vapor compression is one type of refrigeration. In its simplest form, vapor compression involves changing the refrigerant from the liquid to the vapor phase through heat absorption at a low pressure and then from the vapor to the liquid phase through heat removal at an elevated pressure.
While the primary purpose of refrigeration is to remove energy at low temperature, the primary purpose of a heat pump is to add energy at higher temperature. Heat pumps are considered reverse cycle systems because, for heating, the operation of the condenser is interchanged with that of the refrigeration evaporator.
Vapor compression is one type of refrigeration. In its simplest form, vapor compression involves changing the refrigerant from the liquid to the vapor phase through heat absorption at a low pressure and then from the vapor to the liquid phase through heat removal at an elevated pressure.
The art is continually seeking new fluorocarbon based refrigerants and blowing agents that offer alternatives to fluids currently in use. Of particular interest as alternatives are fluorocarbon based compositions that are considered to be environmentally safe substitutes
Ideally, replacement refrigerant compositions possess those properties unique to the composition being replaced including chemical stability, low toxicity, non-flammability, and efficiency-in-use. The latter characteristic is important in refrigeration and air-conditioning applications especially where a loss in refrigerant thermodynamic performance or energy efficiency may have secondary environmental impacts through increased fossil fuel usage arising from an increased demand for electrical energy. Furthermore, the ideal substitute would not require major engineering changes to conventional equipment currently used.
Certain chlorofluoromethane and chlorofluoroethane derivatives have gained widespread use in refrigeration applications including air conditioning and heat pump applications owing to their unique combination of chemical and physical properties. The majority of refrigerants utilized in vapor compression systems are either single component fluids or azeotropic mixtures. Moreover, certain applications, such as centrifugal chillers, and in particular multi-stage centrifugal chillers, can only use pure or azeotropic refrigerants, since nonazeotropic mixtures will separate in pool boiling evaporators, causing undesirable performance.
Previously, 1,1,2,2,3-pentafluoropropane, HFC-245ca, has been proposed as an alternative to 1,1-dichloro-2,2,2-trifluoroethane, R-123, and trichlorofluoromethane, R-11. See N. D. Smith et al., xe2x80x9cR-245ca: A Potential Far Term Alternative For R-11xe2x80x9d, 35 ASHRAE J. 19-23 (1993). The present invention provides additional compounds and compositions that are suitable replacements for R-11 and, in addition, may be used as foam blowing agents.
Mathematical models have substantiated that hydrofluorocarbons, such as 1,1,1,3,3-pentafluoropropane (HFC-245fa), will not adversely affect atmospheric chemistry, being a negligible contributor to ozone depletion and to green-house global warming in comparison to the fully halogenated species.
In accordance with the invention, it has been discovered that the compounds 1,1,1,2,3-pentafluoropropane (xe2x80x9cHFC-245ebxe2x80x9d), 1,1,1,3,3-pentafluoropropane (xe2x80x9cHFC-245faxe2x80x9d), 1,1,2,3,3-pentafluoropropane (xe2x80x9cHFC-245eaxe2x80x9d), and mixtures thereof are useful as refrigerants, heat transfer fluids, and blowing agents. More specifically it has been discovered that these compounds and mixtures meet the need for a nonflammable refrigerant which has a low ozone depletion potential and is a negligible contributor to green-house global warming compared with currently used refrigerants, such as R-11 and 123. Further, it has been discovered that these compounds and mixtures have COPs and capacities that render them suitable for use in refrigeration applications, including in centrifugal chillers, and particularly in multi-stage centrifugal chillers. Also, the compounds and mixtures of the invention exhibit low compressor discharge temperatures.
It has been discovered that the refrigerant HFC-245fa shows unexpected increase in efficiency (also known as coefficient of performance or COP) when compared to CFC-11 in its performance in multi-stage centrifugal chillers.
In one embodiment, the invention provides a method for producing refrigeration using a compound selected from HFC-245eb, HFC-245fa, HFC-245ea, and mixtures thereof In still another embodiment, a method for producing refrigeration using a centrifugal chiller is provided using a compound selected from HFC-245eb, HFC-245fa, HFC-245ea, and mixtures thereof In a preferred embodiment, a method for producing refrigeration using a multi-stage centrifugal chiller is provided using a compound selected from HFC-245eb, HFC-245fa, HFC-245ea, and mixtures thereof In a most preferred embodiment, a method for producing refrigeration using a multi-stage centrifugal chiller is provided wherein HFC-245fa is the refrigerant.
In another embodiment of the invention, a method for producing beating is provided using a compound selected from HFC-245eb, HFC-245fa, HFC-245ea, and mixtures thereof For purposes of this invention, by mixtures is meant both nonazeotropic and azeotrope-like compositions of at least two of the compounds.
Thus, in yet another embodiment, this invention provides azeotrope-like compositions comprising effective amounts of at least two compounds selected from HFC-245eb, HFC-245fa, and HFC-245ea. By effective amount is meant an amount of each component that, when combined with the other component, results in the formation of an azeotrope or azeotrope-like mixture. Preferably, the invention provides azeotrope-like compositions comprising from about 10 to about 90 weight percent 245fa and from about 90 to about 10 weight percent 245ea, the compositions having a boiling point 25xc2x0 C. xc2x17xc2x0 C. at 760 mm Hg. More preferably, the composition comprises from about 30 to about 70 weight percent HFC-245fa and from about 70 to about 30 weight percent HFC-245ea, more preferably about 50 weight percent HFC-245fa and about 50 weight percent HFC-245ea.
For purposes of the invention, by centrifugal chillers is meant refrigeration equipment that uses centrifugal compression to convert the refrigerant gas from low to high pressure. Compression may be performed in a single stage or multiple stages. Preferably the multi-stage operation of the process comprises from about two to about five, more preferably about two to about four and most preferably about two to about three stages of compression. The precise number of stages is application dependent and can be determined without undue experimentation.
For purposes of this invention, azeotrope-like compositions are compositions that behave like azeotropic mixtures. From fundamental principles, the thermodynamic state of a fluid is defined by pressure, temperature, liquid composition, and vapor composition. An azeotropic mixture is a system of two or more components in which the liquid composition and vapor composition are equal at the state pressure and temperature. In practice, this means that the components of an azeotropic mixture are constant boiling and cannot be separated during a phase change.
Azeotrope-like compositions behave like azeotropic mixtures, i.e., or are constant boiling or essentially constant boiling. In other words, for azeotrope-like compositions, the composition of the vapor formed during boiling or evaporation is identical, or substantially identical, to the original liquid composition. Thus, with boiling or evaporation, the liquid composition changes, if at all, only to a minimal or negligible extent. This is to be contrasted with nonazeotrope-like compositions in which, during boiling or evaporation, the liquid composition changes to a substantial degree.
The compounds and mixtures of the invention may be used in a method for producing refrigeration that comprises condensing a refrigerant and thereafter evaporating the refrigerant in the vicinity of a body to be cooled. Alternatively, the compounds and mixtures of the invention may be used in a method for producing heating which comprises condensing a refrigerant in the vicinity of a body to be heated and thereafter evaporating the refrigerant.
In yet another embodiment, the compounds and mixtures of the invention may be used in a method for producing refrigeration using a centrifugal chiller that comprises compressing the compound or mixture of the invention by centrifugal compression and evaporating the refrigerant in the vicinity of a body to be cooled.
In still another embodiment, the compounds and mixtures of the present invention may be used in a method for producing foam comprising blending a heat plasticized resin with a volatile blowing agent comprising the fluids of the present invention and introducing the resin/volatile blowing agent blend into a zone of lower pressure to cause foaming.
In yet another embodiment the compounds and mixtures of the present invention may also be used in a method of dissolving contaminants or removing contaminants from the surface of a substrate which comprises the step of contacting the substrate with the compositions of the present invention. In another embodiment, the compounds and mixtures of the present invention may also be used as fire extinguishing agents.
The compounds and mixtures of the present invention are known materials. Preferably, the materials should be used in sufficiently high purity so as to avoid the introduction of adverse influences upon the cooling or heating properties, constant-boiling properties, or blowing agent properties of the system.
Additional components may be added to the compounds and compositions of this invention to tailor their properties according to the need. For example, in the art, propane and pentane may be added to refrigerant compositions to aid oil solubility and may be added to the fluids of the present invention. Nitromethane may also be added as a stabilizer. Similar materials may be added to the present compositions.
The present invention is more fully illustrated by the following non-limiting examples.